Efficient functioning of the immune system requires a fine balance between cell proliferation and differentiation and cell death, to ensure that the immune system is capable of reacting to foreign, but not self antigens. Integral to the process of regulating the immune and inflammatory response are various members of the Tumor Necrosis Factor (TNF) Receptor/Nerve Growth Factor Receptor superfamily (Smith et al., Science 248: 1019; 1990). This family of receptors includes two different TNF receptors (Type I and Type II; Smith et al., supra; and Schall et al., Cell 61: 361, 1990), nerve growth factor receptor (Johnson et al., Cell 47: 545, 1986), B cell antigen CD40 (Stamenkovic et al., EMBO J. 8: 1403, 1989), CD27 (Camerini et al., J. Immunol. 147: 3165, 1991), CD30 (Durkop et al., Cell 68: 421, 1992), T cell antigen OX40 (Mallett et al., EMBO J. 9: 1063, 1990), human Fas antigen (Itoh et al., Cell 66: 233, 1991), murine 4-1BB receptor (Kwon et al., Proc. Natl. Acad. Sci. USA 86: 1963, 1989) and a receptor referred to as Apoptosis-Inducing Receptor (AIR; U.S. Ser. No. 08/720,864, filed Oct. 4, 1996).
CD40 is a receptor present on B lymphocytes, epithelial cells and some carcinoma cell lines that interacts with a ligand found on activated T cells, CD40L (U.S. Ser. No. 08/249,189, filed May 24, 1994). The interaction of this ligand/receptor pair is essential for both the cellular and humoral immune response. Signal transduction via CD40 is mediated through the association of the cytoplasmic domain of this molecule with members of the TNF receptor-associated factors (TRAFs; Baker and Reddy, Oncogene 12: 1, 1996). It has recently been found that mice that are defective in TRAF3 expression due to a targeted disruption in the gene encoding TRAF3 appear normal at birth but develop progressive hypoglycemia and depletion of peripheral white cells, and die by about ten days of age (Xu et al., Immunity 5: 407, 1996). The immune responses of chimeric mice reconstituted with TRAF3.sup.-/- fetal liver cells resemble those of CD40-deficient mice, although TRAF3.sup.-/- B cells appear to be functionally normal.
The critical role of TRAF3 in signal transduction may be in its interaction with one of the other members of the TNF receptor superfamily, for example, CD30 or CD27, which are present on T cells. Alternatively, there may be other, as yet unidentified members of this family of receptors that interact with TRAF3 and play an important role in postnatal development as well as in the development of a competent immune system. Identifying additional members of the TNF receptor superfamily would provide an additional means of regulating the immune and inflammatory response, as well as potentially providing further insight into post-natal development in mammals.